Re: [PSUBS-MAILIST] VBT positioning

[VBra676539@aol.com]

The early Pisces pumped from a hard tank to an external bladder. You don't 
need to pump it back usually, as the pressure will squeeze the bag. They used 
hydraulic oil, I think, and I've never heard anything nice about it other 
than it worked. It leaked and used bunches of oil and had to be replaced en 
masse when sea water leaked into it. It worked very well, of course, 
otherwise.

Internal bladders: PC-8 started with one, I think. And a couple of small, 60s 
era production subs. They all leaked. The one I know about for sure was a 
local fellow's father down from Indiana with an old psup that had a bladder 
tank. It ruptured while they were testing off Ft. Pierce. All the water ran 
to the stern and stood him more or less on his tail, and then he couldn't 
blow MBTs. The Coasties had to put divers in the water to hoist him and a 
friend out of 60' of water, and they nearly died.

MBTs can be built with a slight rise to the vent position if in fiberglas. 
Steel, too, but harder. The Perry's had their open vents about mid tank 
measured fore and aft, and the vent valves located forward. I'd usually just 
lean back a skosh and push the tail down, which would dump the rest of the 
air. Never had any trouble that way to speak of. The Pisces boats and Leo 
were tail heavy at the surface anyway, so when you opened the main vents they 
tended to settle that way a little bit which emptied the tanks readily 
enough. And the Aquarius had fore and aft saddle tanks, which settled the 
question quite nicely, thank you.

VBTs: Perry's usually had multiple internal tanks, fore and aft, and you 
could pump back and forth, or fill them or discharge them selectively or 
collectively. The 14 series used a double ended T-bottle or thereabouts 
laying in the bilges, vented inboard to fill, blown with high pressure air. 
Aquarius didn't have one at all, and neither do the Nektons. They just hang 
on a small MBT bubble and adjust as necessary. This isn't much of a problem 
in most cases, and most of us nut cases did it routinely.

You can worry about this all you want, but I'd suggest just taking a deep 
breath and jumping in. It SHOULD be a big deal on paper. Get the design right 
initially for CG and CB, then build the boat. It will have its own 
personality, no matter how much thought you put into it. I've noticed that 
the engineers usually gave me something pretty close to what I needed, then 
turned me loose to do the piloting deal on my own. It's the pilot's job to 
turn the built-in idiosyncrasies into positives.

Best Regards.
Vance